Transparent polymer materials with high heat resistance are key materials of the next-generation high-technology industry. They are expected to be widely used in flexible substrates for displays, solar cells and electronic paper, as well as in the aerospace industry and semiconductor industry. In particular, the megatrend of the display, solar cell and electronic paper industries, where the transparent new materials with high heat resistance are used predominantly, in the future will be ubiquitousness with various functions fused, as well as flexibility, large size and high image quality. Accordingly, the demand on the transparent plastic substrate materials with high heat resistance is expected to exceed some 10 billion dollars in 10 years.
Thus, companies in advanced countries, including Ferrania Image Technologies of Italy, Promerus, General Electric (GE) and DuPont of USA, Mitsubishi Gas Chemical, Sumitomo Bakelite and Teijin Films of Japan, and BASF of Germany, are developing transparent optical film materials with high heat resistance for flexible plastic substrate materials.
In terms of morphology, the developed materials may be classified into crystalline polymers and amorphous polymers. Among the materials, the aromatic polyester-based crystalline polymers polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) developed early by DuPont and Teijin Films have relatively low glass transition temperature (Tg) is relatively low with 80 and 150° C., respectively, but the melting temperature (Tm) is very high with 253 and 265° C., respectively. Also, due to their crystalline structure, they are very poorly soluble in solvents and thus it is difficult to prepare transparent films for flexible substrate materials by melting or solvent casting. Besides, mechanical properties such as modulus and coefficient of thermal expansion (CTE) are degraded drastically at temperatures higher than the Tg of the polymer materials. That is, the modulus decreases whereas CTE (ppm/° C.) increases. Accordingly, in order to use PET or PEN for flexible plastic substrate materials, it is required to modify the mechanical properties using glass fiber and coat both sides of the substrate material with acrylate-based cross-linked polymers to reduce water absorption and oxygen permeability.
For use as the flexible plastic substrate material for next-generation displays, solar cells, electronic paper, etc., active matrix (AM) type high-quality display should be realizable. In order to realize the AM display, conductive indium tin oxide (ITO) should be deposited on a transparent plastic substrate material at high temperature of 180° C. or above and a silicon substrate type, highly integrated thin-film transistor (TFT) should be fabricated. Accordingly, amorphous polymer materials with new structure having superior heat resistance, low CTE and hygroscopy, good transparency and good film formability have been developed.
Examples include Ferrania's polyacrylate (PAR) polymers, Promerus' cycloolefin polymers (COP/COO), GE and Mitsubishi Gas Chemical's polyimide (PI) polymers, and Sumitomo and BASF's polyether sulfone (PES) polymers.
Among them, Promerus' cross-linked polynorbornene COP (product name: Appear 3000) has good Tg, light transmittance and hygroscopy, but has a very high CTE. In contrast, Ferrania's PAR (product name: Arylite) has good Tg, light transmittance and hygroscopy, as well as very low CTE at high temperatures. Mitsubishi Gas Chemical's PI (product name: Neopulim L-3430) has good Tg and light transmittance as well as very superior CTE at high temperature, but hygroscopy is very high. And, Sumitomo's PES has relatively low Tg, but good light transmittance and hygroscopy and very superior CTE at high temperature.
In Korea, I-Component has developed optical films for display substrates using BASF's PES resin.